Improving development workflow using Git Hooks

Git hooks are scripts that are triggered at certain points in git’s execution. Think of git hooks as a program which runs before/after a predefined action.There can be client or server side hooks.Client-side hooks are triggered by operations such as committing and merging, while server-side hooks run on network operations such as receiving pushed commits.

Here are some of the git hooks

• prepare-commit-msg – Provide a default commit message if one is not given.
• pre-commit – Runs before git commit
• commit-msg – Commit message validation.
• post-commit – Runs after a successful commit.
• pre-push – Runs before git push after the remote is verified to be working. It takes 2 arguments: the name of the remote and the URL to it.
• pre-rebase – Runs before git rebase.
• post-checkout – Runs after a successful checkout.
• post-merge – Runs after a successful merge

Why should you use a git hook?

Any custom script can be placed in any of the git hooks.This will ensure the developer follows a set of guidelines during the development process. For example, a company policy states that no function should have more than 50 lines of code.Just place this guideline in form of a script in a pre-commit hook.

Git hooks are also very helpful in preventing what is called as a Commit Porn.Commit messages like Fix some issues can easily be prevented by enforcing a proper format to the commit messages. (See more of commit porn — http://whatthecommit.com/ , keep on refreshing to see new messages)

Or Git hooks can be used to enforce that code formatting is according to the company’s style guide principles.

These are only some of the many examples which developers can use to improve their development workflow.

How to set up a git hook?

By default the hooks directory is $Project_Root/.git/hooks We will update pre-commit hook to enforce style guides for Javascript using jshint.

1. Install jshint in your system.
   Run npm install --save-dev jshint
2. To use any git hook we must remove the .sampleextension.
   Rename pre-commit.sample to pre-commit.Now pre-commit hook is active.
3. Copy the following code and paste in the pre-commitfile.

#!/bin/sh
echo "pre-commit started"
files=$(git diff --cached --name-only --diff-filter=ACM | grep ".js$")
if [ "$files" = "" ]; then 
    exit 0 
fi

pass=true

for file in ${files}; do
    result=$(jshint ${file})
    if [ $? == 0 ]; then
        echo "\033[32mJSHint Passed: ${file}\033[0m"
    else
        echo "\033[31mJSHint Failed: ${file}\033[0m"
        echo "\033[31m$(jshint ${file} | sed '$d' | sed '$d')\033[0m\n"
        pass=false
    fi
done

if ! $pass; then
echo "\033[41mCOMMIT FAILED:\033[0m Please install JSHINT(if not installed) and then make sure there are no JSHINT errors \n"
    exit 1
fi

The above script runs on each of the javascript file modified and then runs jshint to check for style guidelines errors. The style guidelines can be put in .jshintrc file at the root level of your project.
Refer : http://jshint.com/docs/

As the last step you should set proper permissions for your git hook to run.
Run chmod +x .git/hooks/pre-commit

That’ it . Now if the developer commits and there are some jshint style violations , git will throw an error.

How to share git hooks ?

Git Hooks are not shared.This means that you cannot push them or pull it from/to a remote repository.However, you can create symbolic link — :

1. Create a folder named hooks in your project at root level
2. Add a file named pre-commit and write your hook script in it.
3. Run ln -s -f ../../hooks/pre-commit ./git/hooks/pre-commit

By this way, the hooks can also be under version control.Anyone who clones your repo should run the above command for the pre-commit hook to be activated.

Git hooks are extremely powerful and can help you automate your workflow to a large extend.
Are you using git hooks in a cool way? Let me know in the comments.